1. Field of the Invention
The present invention relates to a multicast message communicating system, a multicast message communicating apparatus, a base station apparatus, and mobile stations for use with a mobile communicating system for controlling transmission powers of the mobile station and the base station in the case that the base station transmits a multicast message to the mobile stations using a multicast channel.
2. Description of the Related Art
There are many methods for optimizing transmission powers of a base station and a plurality of mobile stations for use with mobile communicating systems. In particular, in the DS-CDMA system of which a plurality of channels is transmitted and received with one frequency band, a plurality of cells may be adjacently disposed. Thus, it is necessary to prevent one cell from interfering with other cells. In addition, to stably transmit and receive signals between a base station and mobile stations in the local cell, it is necessary to optimize not only a transmission power from the base station to the mobile stations and transmission powers of the mobile stations to the base station.
For example, Japanese Patent Laid-Open Publication No. 7-336292 discloses a method for maintaining a sufficient transmission quality over a communication link. This method comprises the steps of (a) calculating the gain of a signal path between a transmitting device and a receiving station, (b) measuring the level of the interference power of a common communication path of the receiving station, (c) calculating the product of the reciprocal of the gain of the signal path, the level of the interference power of the common communication path, and a predetermined value corresponding to the minimum target value of the ratio of the received carrier power and the common communication interface power, (d) adjusting the power of a signal transmitted by the transmitting device corresponding to the product, and (e) repeating the steps (a) to (e) by varying a time interval of the step (d). Thus, the necessity of the coincidence and the linkage of a plurality of transmitting devices can be alleviated. Thus, the cost of the transmission power controlling process can be reduced.
As another related art reference, Japanese Patent Laid-Open Publication No. 8-32513 discloses a transmission power controlling method for a spread spectrum communicating apparatus. This method comprising the steps of (a) storing a predetermined transmission power control amount corresponding to the number of reception times of the same value of a transmission power control bit that is transmitted from a receiving station to a transmitting station, the predetermined transmission power control amount being stored to the transmitting station, (b) successively transmitting the transmission power control bit from the receiving station to the transmitting station, (c) detecting the number of reception times of the same value of the transmission power control bit transmitted from the receiving station, the number of reception times being detected by the transmitting station, and (d) controlling the transmission power corresponding to the transmission power control amount corresponding to the number of reception times of the same value of the transmission power control bit, the transmission power being controlled by the transmitting station, wherein when the transmission power control bit of the same value is successively received, it is determined that the reception power of the remote station has been largely varied and the transmission power is largely increased or decreased as the reception time elapses, thereby compensating the abrupt fluctuation of the communication path.
As other related art references, Japanese Patent Laid-Open Publication Nos. 9-275373 (Japanese Patent No. 2803626) and Japanese Patent Laid-Open Publication No. 10-224293 disclose controlling systems and controlling methods for controlling a transmission power of a radio signal corresponding to the code division multi-access (CDMA) system. In these systems and methods, when a local station receives a transmission power increase/decrease command from a radio base station controlling device, the local station transmits a signal that represents an increase/decrease amount designated by an output increase/decrease designating means to a transmission output controlling means of the mobile station.
In conventional cellular mobile communicating systems, there are two types of channels transmitted by the base station. The first type of channels is a discrete (multicast) channel assigned to each specified user (mobile station). The second type of channels is a common (broadcast) channel with which all users receive control information. Although a common (broadcast) channel that a plurality of nonspecific users can receive and use control information has been defined, a multicast channel that a plurality of specific users can receive has not been defined. Thus, in the conventional cellular mobile communicating systems, to perform a multicast service, the same information is transmitted to individual users with discrete (multicast) channels. Alternatively, a broadcast message is transmitted to specific users with the common channel.
On the other hand, in the next generation mobile communicating systems that are being currently standardized (third and later generation systems), it is expected that such a multicast service using a multicast channel will be provided. In particular, when a CDMA cellular system using spread spectrum method is considered, it is necessary to maximally suppress a multicast message from interfering with other channels. In other words, it is preferred that the reception power of a multicast message of a mobile station is the minimally required level for a user whose reception condition is the worst in specific users who receive the multicast message.
The present invention is made from the above-described point of view. An object of the present invention is to allow the quality of a multicast message transmitted from a base station to a plurality of specific mobile stations to be improved in a short time and the power consumption necessary for controlling the transmission powers of mobile stations to be decreased.
A first aspect of the present invention is a multicast message communicating system, comprising a base station for transmitting a multicast message using a multicast channel, and a plurality of mobile stations for receiving the multicast message from the base station, wherein the base station has a receiving portion for receiving transmission power increase request signals from the plurality of mobile stations corresponding to reception powers of the multicast message received from the plurality of mobile stations, a reception power detecting portion for detecting the reception powers of the transmission power increase request signals received from the receiving portion, a transmission power control generating means for deciding and generating a transmission power increase request signal or a transmission power decrease request signal for the plurality of mobile stations corresponding to the received powers, and a power controlling portion for controlling the transmission power of the multicast message transmitted to the plurality of mobile stations corresponding to the reception powers, wherein the multicast message and the transmission power increase request signal or the transmission power decrease request signal are transmitted to the plurality of mobile stations, and wherein the plurality of mobile stations gradually decrease the transmission powers of the transmission power increase request signals corresponding to the reception powers of the transmission power increase request signal or the transmission power decrease request signal, and the multicast message received from the base station.
A second aspect of the present invention is a multicast message communicating method having a base station for transmitting a multicast message using a multicast channel and a plurality of mobile stations for receiving the multicast message from the base station, the method comprising the steps of (a) receiving transmission power increase request signals from the plurality of mobile stations corresponding to reception powers of the multicast message received from the plurality of mobile stations, (b) detecting the reception powers of the transmission power increase request signals received from the receiving portion, (c) deciding and generating a transmission power increase request signal or a transmission power decrease request signal for the plurality of mobile stations corresponding to the received powers, and (d) controlling the transmission power of the multicast message transmitted to the plurality of mobile stations corresponding to the reception powers, wherein the steps (a) to (d) are performed by the base station, wherein the multicast message and the transmission power increase request signal or the transmission power decrease request signal are transmitted to the plurality of mobile stations, and wherein the plurality of mobile stations gradually decrease the transmission powers of the transmission power increase request signals corresponding to the reception powers of the transmission power increase request signal or the transmission power decrease request signal, and the multicast message received from the base station.
A third aspect of the present invention is a base station for transmitting a multicast message to a plurality of mobile stations using a multicast channel, comprising a receiving portion for receiving transmission power increase request signals from the plurality of mobile stations corresponding to reception powers of the multicast message received from the plurality of mobile stations, a reception power detecting portion for detecting the reception powers of the transmission power increase request signals received from the receiving portion, a transmission power control generating means for deciding and generating a transmission power increase request signal or a transmission power decrease request signal for the plurality of mobile stations corresponding to the received powers, and a power controlling portion for controlling the transmission power of the multicast message transmitted to the plurality of mobile stations corresponding to the reception powers, wherein the multicast message and the transmission power increase request signal or the transmission power decrease request signal cause the transmission powers of the plurality of mobile stations to be increased or decreased, and wherein the plurality of mobile stations gradually decrease the transmission powers of the transmission power increase request signals corresponding to the reception powers of the transmission power increase request signal or the transmission power decrease request signal, and the multicast message received from the base station.
A fourth aspect of the present invention is a mobile station for receiving a multicast message from a base station using a multicast channel, comprising a receiving portion for receiving the multicast message and a transmission power increase request signal or a transmission power decrease request from the base station, a reception power detecting portion for detecting the reception power of the multicast message received from the receiving portion, and a power controlling portion for comparing the reception power with a predetermined threshold value, stopping transmitting the transmission power increase request signal to the base station when the reception power is larger than the predetermined threshold value, and increasing the transmission power of the transmission power increase request signal when the reception power is equal to or smaller than the predetermined threshold value and the receiving portion receives the transmission power decrease request signal, wherein when the power controlling portion stops transmitting the transmission power increase request signal to the base station, the power controlling portion gradually decreases the transmission power thereof.
According to the multicast message communicating system of the present invention of which a base station transmits a multicast message to a plurality of message with a particular channel, the reception powers of the mobile stations quickly converge to optimum values. In addition, the power consumption of transmission power control signals transmitted by the mobile stations can be decreased.
With reference to FIG. 1, according to the present invention, in a mobile station, a power measuring device 24 detects the reception power of a multicast message. A transmission power control signal detecting device 25 detects a transmission power control signal transmitted from a base station. Corresponding to the detected results, a transmission power controlling device 26 decides the transmission power of a transmission power increase request signal transmitted to the base station. At this point, when the reception power of the multicast message is equal to or larger than a predetermined threshold value, it is not necessary to transmit the transmission power increase request signal (the transmission power controlling device 26 decreases the transmission power of the transmission power increase request signal to 0). However, since this signal is transmitted with a common channel of all mobile stations, even if the reception power becomes equal to or larger than the predetermined threshold value, the transmission power controlling device 26 gradually decreases the transmission power. Thus, the reception power of the multicast message quickly converges to the optimum value. As a result, the power consumption of the mobile stations can be decreased.